this is what works great on my 557cid/650's. hardin thermostatic filter mount and 3x20 oil cooler. simple setup and i can run hard and never see my oil temp over 210.
https://cimg1.ibsrv.net/gimg/www.off...bbfb6b1f76.jpg

For those that have larger cooler, are you running a standard single stage mercruiser water pump?

Yes, Standard pump

Yes, single stage here

I run the 3"x18" earlier mentioned. 454's 600 HP. Similar mounting as Saber28. I don't see temps over 180°F
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https://cimg6.ibsrv.net/gimg/www.off...30278f51f8.jpg

So looked at engine and checked oil cooler no clogs. Oil cooler is standard 502 2x12 and goes to power steering cooler. I have never ordered an oil cooler so looking for more guidance lol.. teaching myself. Anyhow, 502 gen v 550 hp.. help, please :-)

If you can be sure the cooler came off a working motor without a failure then you can get a used cooler. If the motor had failed prior, there is no kind of flushing other then to take apart to ensure all the metal has been cleaned out.

Opinion
If you can find a good used 2 3/4 x 18 Merc 500 cooler it should work just fine without a thermostat. If you get a larger one and do not have a thermostat then the oil can stay to cool so moisture may not be removed during running. Can get a larger one with a thermostat so the oil can reach at least 212*

BS DON"T buy a used oil cooler, people actually lie about the history of parts. It's your engine do as you please. I have already posted links for the correct oil coolers, do as you wish. Good luck with used metal particles in your oil!

GLENAMY- i definitely would not buy used. I actually went back and bought the oil cooler you mentioned. I appreciate you commenting and adding the link! Hopefully this $1500+ investment gives me 210-220 temps!!

BS please read the Fing comment
Mine is used and came from a OSO guy I trust, and has been working just fine